> That’s what I was saying.  But you seemed to imply that grep -F 'musl'
> was preferable to grep -E '^musl' from a portability and robustness
> point of view.

Sorry if I was unclear; `grep -F` is preferable to `fgrep` since the latter is less portable, and `grep -F` may be preferable to `-E` because it avoids the undesirable zsh expansion.

> > The -q is superfluous with the >/dev/null, and should be removed;
> > incidentally though, is it not harmless in this case?
>  It is not.  In Thomas’ case, using grep >/dev/null would have avoided
> a 0 exit status and thus prevented his system from being erroneously
> detected as supporting musl.

I may have misunderstood Thomas' case, where zsh expands ^musl to all filenames not containing `musl`. For convenience, here's the sample we were discussing, which would be a different case:

if command -v ldd >/dev/null && ldd --version 2>&1 | grep -Fq 'musl' >/dev/null

In this case there ought to be no expansion because there is no carat and we use `grep -F`.

Generally speaking `grep -q` can have undesirable side-effects, but I cannot see how such would occur in this case since all the input to grep is from the pipe, which barring a radically improbable interrupt should never error.  I would be interested to know if I have misunderstood, though.

On Tue, 10 Apr 2018 at 16:56 Arthur Reutenauer <arthur.reutenauer@normalesup.org> wrote:
On Tue, Apr 10, 2018 at 11:05:12AM +0000, Brian Hunt wrote:
>>  The caret in itself was not the problem, only that it was not escaped
>> for the shell.  Testing a regexp, with -E of course, is just as robust,
>> and allows us to be more specific about what we test.
>
> Either is fine I am sure

  That’s what I was saying.  But you seemed to imply that grep -F 'musl'
was preferable to grep -E '^musl' from a portability and robustness
point of view.

>>  grep -E '^musl' works just as well; and as I explained, -q may return 0
>> even if there are errors, so should be avoided.
>
> The -q is superfluous with the >/dev/null, and should be removed;
> incidentally though, is it not harmless in this case?

  It is not.  In Thomas’ case, using grep >/dev/null would have avoided
a 0 exit status and thus prevented his system from being erroneously
detected as supporting musl.

        Best,

                Arthur
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